The First Australopithecus, 1925

The discovery of the 2.5-million-year-old Taung Child skull marked a turning point in the study of human brain evolution.

By Sabrina Richards | July 1, 2012

FIRST OF ITS KIND: Raymond Dart’s classification of the approximately 2.5-million-year-old Taung Child skull as an upright-walking hominin was met with skepticism by contemporaries who argued its brain size was too small to merit such a classification.Science Source

FIRST OF ITS KIND: Raymond Dart’s classification of the approximately 2.5-million-year-old Taung Child skull as an upright-walking hominin was met with skepticism by contemporaries who argued its brain size was too small to merit such a classification. SCIENCE SOURCE

Australian anatomy professor Raymond Dart was adjusting the collar of his dress suit in preparation for a friend’s wedding when a box, shipped from a limestone quarry near Taung, South Africa, arrived at the doorstep of his Johannesburg home in November 1924. Dart abandoned his collar to dig through the package’s contents—all the while ignoring the grumblings of his wife and the groom, who were anxious to begin the wedding ceremony. Inside the box, he found a fossilized mold of a brain and a matching child’s skull partially buried in stone. Dart quickly realized the significance of the finding, and by February 1925 had published an article in Nature identifying a new species: Australopithecus africanus. The 2.5-million-year-old “Taung Child” or “Taung Baby,” as Dart called it, was the first member of the Australopithecus genus discovered, and it challenged contemporary ideas about human evolution.

According to the era’s prevailing view— “proven” by the anatomy of the Piltdown specimen, which was later unmasked as a hoax—increases in brain size preceded the emergence of other human attributes during early hominin evolution. While the Taung skull had human-like characteristics such as small canines, a steep forehead, and a spinal cord alignment that suggested bipedalism, Taung’s brain size was closer to that of a nonhuman ape. The fossil “heralded a new direction” in the study of human evolution, says Kieran McNulty, a paleoanthropologist at the University of Minnesota, by providing evidence that changes in brain size lagged behind the development of a human-looking face and upright walking. Nevertheless, the fossilized endocranial cast, or endocast, suggested to Dart that Taung’s brain was beginning to reorganize in recognizably human ways. Dart calculated that the ratio of cerebral cortex to cerebellum in Taung’s brain was larger than in gorillas and chimpanzees and also noticed that a groove on the outside of the brain, the lunate sulcus, appeared to have moved backward into a position closer to that seen in humans.

Although Dart’s discovery instantly made him famous, many anthropologists met his interpretations with extreme skepticism. The study of human evolution was still in an “embryonic stage,” says Goran trkalj, a biological anthropologist at Australia’s Macquarie University. Taung’s small brain flouted orthodox theories, leading some anthropologists to group the extinct species with gorillas and chimpanzees. It wasn’t until 1932 that A. africanus was classified as a hominin, and not until the 1940s, as more Australopithecus fossils were identified, that the field began to accept Taung.

Scientists are still learning from the Taung skull and endocast. In humans, a seam along the frontal bone closes slowly because the brain expands rapidly after birth. But in nonhuman apes, it fuses and ossifies quickly. Taung, now estimated to be about 3 or 4 years old at the time of death, retains this “persistent metopic suture,” suggesting its brain development had already diverged from that of the other apes, says Dean Falk, who studies the evolution of cognition at Florida State University. But many unanswered questions of developmental timing and patterns remain, says McNulty. “We’ll be looking at Taung for decades to come.”

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The discovery of the Taung Child fossil was a pivotal event in the history of paleoanthropology.Â To underscore this, there are several things upon which the article could have expanded.i) The Taung Child is a double "type specimen" -- Dart described the fossil as not just the first specimen of a new genus, Australopithecus, but also the first known example of a new species, A. africanus.Â The fact that the fossil represents the remains of an immature individual makes its type specimen status something of a rarity in taxonomic terms (generally,Â the description of a type specimen will be based on an adult individual).ii) The Taung Child was also the first fossil hominin to be discovered in Africa.Â Ultimately, this had the effect (by the 1940s, as the article notes), of turning the attention of paleoanthropologists away from Europe (where neandertals had been discovered inÂ Germany's Neander Valley inÂ 1856, and the first evidence of early modern humansÂ had been discovered at the Abri de Cro-Magnon rock shelter in France, in 1868), and from Asia (where fossils eventually attributed to Homo erectus had been discovered in Java in 1891 and China,Â from 1921 throughÂ the 1930s), as the regions providing the earliest evidence of human ancestry.Â The Taung Child, and the australopithecine fossils found subsequently, made it clear that the human lineage traced its earliest ancestral origins back to Africa.iii) The point that, "Scientists are still learning from the Taung skull and endocast.", is well-taken.Â As recently as 2006-07, Lee Berger and Scott McGraw produced convincing comparative evidence that the Taung Child was likely a victim of predation by a very large raptor (which would help explain why the Taung Child is still the only hominin fossil to have been recovered from the Taung site, despite repeated excavations).